Written By Bernard Leavitt, Indium Corporation
The demand for hermetic packages that house laser diodes is growing, and companies that traditionally made RF/microwave packages are now expanding their businesses into optical packages.
What makes optical package manufacturing unique is the variety of end uses and operational temperatures. As a result, the assembly materials options have to be broad. Gold solder alloys provide low and high temperature options.
Here is a quick overview of the most commonly used gold alloys for package assembly (all eutectic or near-eutectic):
- 80Au20Sn (280°C): This alloy wets very well in a forming gas atmosphere and has a eutectic melting temperature of 280°C .
- 88Au12Ge (356°C): This alloy is slightly prone to voiding, so it’s typically not used in glass-to-metal joints. Some companies use 88Au12Ge window frame preforms in the baseplate-to-frame joint. Locating leaks and doing re-work on baseplate-to-frame joints is fairly easy, depending on the size of package.
- 80Au20Cu (891°C): This is also a eutectic alloy which makes it ideal for braze joints that are dependent on capillary action to fill them, like glass-to-metal joints.
Some company’s reference 80Au20Sn and 88Au12Ge as low-temperature brazes because they are used for hermetic sealing packages with low operating temperatures. 80Au20Sn is commonly used for Kovar lid attachments.
Summary: Gold solder alloys are very important due to their unique range of reflow temperatures and their resistance to corrosion. This makes them ideal for high-reliability optical and laser hermetic package housing assemblies.
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